Low vaccination rates are likely responsible for the large measles outbreak that began at Disneyland in California last December, a new analysis suggests. The researchers estimated that the MMR (measles, mumps and rubella) vaccination rate among the people who were exposed to measles in that outbreak may be as low as 50 percent, and is likely no higher than 86 percent. Since the beginning of this year, 127 cases of measles in the United Stateshave been linked to the Disneyland outbreak, according to the Centers for Disease Control and Prevention (CDC). Because measles is such a highly contagious virus, vaccination rates of 96 percent to 99 percent are necessary to prevent outbreaks, Majumder said.